This invention relates to earphones in general and, in particular, to a new and useful closed earphone construction, wherein the sound-emitting diaphragm bears tightly on the ear of the wearer with its front side by means of a circum-aural or supra-aural coupling space, and the backside of the diaphragm is coupled with at least one soundproof cavity.
A soundproof cavity, in accordance with the invention, supplies a relatively high restoring force to the diaphragm, particularly when the earphone is flat, for reasons of form design. Ear cushions and the soundproof cavity have the effect that noises coming from the outside cannot penetrate to the ear, and they also prevent sound produced by the earphone from escaping to the outside. Measurements of the sound absorption have shown, however, that ear cushions have only a slight sound absorption for low frequencies, while the absorption values in the remaining frequency range are about 20 db.
Both the permeability of the ear cushions for sound waves of low frequency and the restoring force of the volume of air in the soundproof cavity cause a drop of the frequency curve below 200 Hertz.